SiAlONs are grouped into α-SiAlONs and β-SiAlONs. α-SiAlONs, oxynitride materials represented by General Formula: Si12-(m+n)Al(m+n)OnN16-n, give a phosphor when they are solid-solubilized with a rare earth element and the structure is stabilized when they contain a solid-solubilized metal element. Examples of the metal elements traditionally solid-solubilized for stabilization of the structure of the phosphor's host crystal include Li, Ca, Mg, Y, and the like (see Patent Documents 1 to 4).
Patent Document 1 discloses a Ca-solid-solubilized α-SiAlON phosphor represented by General Formula: CaxEuySi12-(m+n)Al(m+n)OnN16-n (wherein, x and y each are a value of more than 0 and less than 2; x+y is a value of more than 0 and 2 or less; m is 2(x+y) and n is a value of 0.5 or more and 2 or less). As described for the phosphor described in Patent Document 1, it is possible to make the stable structure in a wide compositional range and obtain high luminous efficiency when Ca2+ is used as the metal ion for stabilization of the structure. In contrast, Patent Documents 2 to 4 disclose Li-solid-solubilized α-SiAlON phosphors containing Li+ as the metal ion for stabilization of the structure.